This invention relates generally to thermal spray processes and more particularly to powder port blow-offs for plasma spray faceplates. In plasma spray processes, a plume of plasma is used to apply a coating material to a substrate. The plasma plume is created by passing a gas such as nitrogen through an electric arc, which creates a very high temperature stream of plasma, which is then directed toward the substrate. The coating material is injected into the plasma stream typically in the form of a powder near the plasma source. The powder is melted and projected towards the substrate thereby forming a layer of the sprayed material on the substrate.
The powder is typically injected into the plasma stream by one or more powder ports mounted on a faceplate radially around the circumference of an opening, or nozzle, from which the plasma plume is emitted. In other embodiments, powder ports are arranged in a semi-radial configuration in which the powder ports are inclined forward or rearward with respect to the plasma plume. During the thermal spray process, powder coating material inherently accumulates on the faceplate, including the nozzle. Particularly when multiple powder ports are employed, it is typical that the powder streams foul up opposing powder ports. Therefore, powder port blow-offs are used to blow powder not consumed in the plasma plume into the surrounding air, whereby it can be collected by air filters. Powder port blow-offs are typically located near the powder ports, and comprise nozzles that project a jet of air towards the plasma plume.
Nonetheless, powder still accumulates on the faceplate, powder ports and blow-offs. Additionally, in previous powder port blow-off designs, the powder ports were directed inward toward the faceplate. This resulted in blow-back of powder coating material onto the faceplate, instead of being directed away from it. Accumulated powder on the faceplate or other components requires intermittent shutdowns of the coating process so the powder ports, blow-off nozzles and faceplate can be cleaned, which slows production rates. Additionally, the stoppages require that the plasma gun and powder feeders be shut down and restarted more often, which wastes expensive powders, gasses, and electricity; and reduces plasma spray gun component life. With previous blow-off designs, shutdowns may be required as often as every ten spray cycles. With some parts requiring as many as seventy spray cycles to completely coat all components of the part, that is far too many shutdowns. Therefore, there is a need for a more effective powder port blow-off system that results in fewer production stoppages.